Iron regard to the general arrangement of stairways and the proportions of the steps, reference will again be made to what has already been said in the section on Stone Construction (p. 3S); it will, therefore, only remain to consider the special arrangements necessitated by the use of iron. It must first of all be observed that for iron stairways wood or stone construction is more or less taken as the model—the former more particularly w-lien wrought iron is employed, the latter exclusively when cast iron is used.
The characteristic feature in cast-iron stairs is that each step is cast in one piece, and is connected with the neighboring steps by screw bolts which are sometimes made as the continuation of tbe balusters; in tbis case the screw bolts pass through a ring cast on the end of the step. It need hardly be said that the steps are not solid masses, as is the case when stone is used, but are thin walls; so that the lower or rear sides remain open. The treads and risers have also large perforations. Instead of Imiting the steps at their ends by screw bolts in one piece with the balusters, two strips 2 I0 2 inches wide may be cast along the length of each step, like the oblique rabbets on geometrical stairs, each of which is made to lie upon a corre sponding strip of the next, step, and is screwed fast to it in several places.
This method is mostly employed on the small scale, 1.vith steps, sav, 3 feet in length for back- staircases in winding form. In this case the spindle is cast on each step in the form of a hollow cylinder of equal height with the step—an arrangement corresponding to that so often seen in winding stone stairs. The spindle pieces are rebated to one another above and below, and form a column which bas a substantial foundation below and firm con nection with the ceiling above.
A stair built in this fashion is shown in Fig-ure (p. 6). It will readily be seen that the construction allows a very light and pleasing treat ment, and that contact with the wall is not necessary. The thickness of the metal in a case tbe one delineated may be 95– of an inch for the treads and the spindle pieces; for the risers, 2Y? inches. In straight iron stairs the other form of construction is preferred—namely, the step is made in two pieces, as in 1.vooden stairs, and these pieces are rebated together. They are then screwed, by the aid of three-sided and usually perforated accessory pieces, upon iron cheeks having the form of the I-beam.